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Steric trends and kinetic parameters for radical reductions involving alkyldiphenyltin hydrides
Journal article   Peer reviewed

Steric trends and kinetic parameters for radical reductions involving alkyldiphenyltin hydrides

D. Dakternieks, D.J. Henry and C.H. Schiesser
Journal of Physical Organic Chemistry, Vol.12(3), pp.233-239
1999
DOI: https://doi.org/10.1002/(SICI)1099-1395(199903)12:3<233::AID-POC117>3.0.CO;2-T
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Abstract

Absolute rate constants and Arrhenius parameters for hydrogen atom abstraction by primary alkyl radicals from methyldiphenyl-, ethyldiphenyl-, butyldiphenyl-, isopropyldiphenyl-, cyclohexyldiphenyl- and (trimethylsilyl)methyldiphenyltin hydride were determined in tert-butylbenzene through utilization of the ‘5-hexenyl radical clock’ reaction. At 80 °C, rate constants (kH) for all hydrides were found to lie in the range (8.2–11.5) × 106 lmol−1 s−1, with similar Arrhenius expressions for all reactions studied [viz. log kH = (8.92–8.97)−(3.03–3.24)/2.3RT]. The nature of the alkyl substituent appears to have a subtle effect on the function of the hydride such that the order or reactivity of stannanes (RPh2SnH) is Me > Et > Bu > i-Pr > c-Hex ≥ Me3SiCH2; this trend can be directly traced to steric effects operating in the transition states for hydrogen transfer from tin to carbon. The implications of these observations are discussed.

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